Global and domestic demand for fossil fuels continues to rise despite price increases and other economic and geopolitical concerns. As such demand continues to rise, research and investigation into finding additional economically viable sources of fossil fuels correspondingly increases. Historically, many have recognized the vast quantities of energy stored in oil shale, coal and tar sand deposits, for example. However, these sources remain a difficult challenge in terms of economically competitive recovery. Canadian tar sands have shown that such efforts can be fruitful, although many challenges still remain, including environmental impact, product quality, and process time, among others.
Estimates of world-wide oil shale reserves range from two to almost seven trillion barrels of oil, depending on the estimating source. Regardless, these reserves represent a tremendous volume and remain a substantially untapped resource. A large number of companies and investigators continue to study and test methods of recovering oil from such reserves. In the oil shale industry, methods of extraction have included underground rubble chimneys created by nuclear explosions, in-situ methods such as In-Situ Conversion Process (ICP) method (Shell Oil), and combustion within steel fabricated retorts. Other methods have included in-situ radio frequency methods (microwaves), and “modified” in-situ processes wherein underground mining, blasting and retorting have been combined to make rubble out of a formation to allow for better combustion and heating permeability. Permeability is generally desired because pyrolysis, the method by which the hydrocarbons are extracted, can be achieved with greater quality and production with lower energy input.
Among typical oil shale processes, all face tradeoffs in economics and environmental concerns. No current process alone satisfies economic, environmental and technical challenges. Moreover, global warming concerns give rise to additional measures to address carbon dioxide (CO2) emissions which are associated with such processes. Methods are needed that accomplish environmental stewardship, yet still provide high volume energy fuel output.
Below ground in-situ concepts emerged based on their ability to produce high volumes while avoiding the cost of mining. While the cost savings avoiding mining can be achieved, the in-situ method requires heating a formation for a longer period of time due to the extremely low permeability of shale, which by its nature, requires a slower and longer retorting time to fracture and convert hydrocarbons in a formation. By utilizing the in-situ method, gains can be realized in the volume and mining cost savings, but the in situ method runs into permeability problems requiring formation fracture and longer periods of time to produce oil and gases. Perhaps the most significant challenge for any in-situ process is the uncertainty and long term potential of water contamination that can occur with underground freshwater aquifers. In the case of Shell's ICP method, a “freeze wall” is used as a barrier to, in theory, keep separation between aquifers and an underground treatment area. Although this is possible, no long term analysis has proven for extended periods to guarantee the prevention of contamination. Without guarantees and with even fewer remedies should a freeze wall fail, other methods are desirable to address such environmental risks.
For this and other reasons, the need remains for methods and systems which can provide improved recovery of hydrocarbons from suitable hydrocarbon-containing materials, which have acceptable economics and avoid the drawbacks mentioned above.